Rebound preventing means in air blast circuit breaker



H.. FORWALD Filed Feb. 23, 1961 May 26, 1964 REBOUND PREVENTING MEANS INAIR BLAST CIRCUIT BREAKER INVENTOR. HAflkM/ Era/AM 7 BY ,JM, fi fimvav3,134,875 REBOUND PREVENTING MEANS IN AIR BLAST CIRCUIT BREAKER HaakonForwald, Ludvika, Sweden, assignor to Allmiinna Svenska ElektriskaAktiebolaget, Vasteras, Sweden, a

corporation of Sweden Filed Feb. 23, 1961, Ser. No. 91,210 Claimspriority, application Sweden Feb. 27, 1960 2 Claims. (Cl. 200-148) Thisinvention relates to air blast circuit breakers, and more specificallyrelates to a novel means for controlling the opening speed of themovable contact of an air-blast circuit breaker.

In air blast circuit breakers which are well known 'to those skilled inthe art, the velocity of the movable contact normally increases linearlywith time. Therefore, when the contact reaches the end of its openingstroke, its velocity is quite high so that the kinetic energy of themovable contact is appreciable. This requires a braking means which canabsorb the substantial kinetic energy of the movable contact withoutcausing substantial bounce. In the past, it has been the practice, forexample, to let the contact strike a rubber buffer at the end of itsopening motion. However, because of the relatively short distance whichthe rubber buffer would permit the contact' to move and because'of thehigh kinetic energy of the contacts, exceedingly large impulse forceswere developed which require strong structural elements to withstandthese impulse forces, and which produce bouncing problems which are verydifficult to eliminate.

Another attempted solution to this problem has been to decrease themovable contactvelocity toward the end of its stroke. Since the kineticenergy developed in the movable contact is proportional to the square ofits velocity, even a relatively small decrease in the velocity of themovable contact at the end of the stroke can result in a substantialdecrease of the impulse forces generated when the contact is brought toa stop.

In order to provide this decrease in velocity, it has been 1 thepractice to secure a piston to the movable contact which moves within acylinder.

7 As the movable contact moves towards its disengaged position, thecylinder compresses the air Within an enclosed-cylinder space so that aconstantly increasing restraining vforce is developed tending to retardthe speed of the contact asit comes closer and closer to its endposition.

It has been found that this arrangement has a serious disadvantageinthat shock waves are generated through the compressed air cushionwhich serves as a damping air cushion which cause very serious bouncingproblems when the contact'reaches its end position, which bouncingproblems could result in restrikeof the arc.

In accordance with the present invention, a means is provided forcontrolling the velocity of the movable contact at the end ofit's's'troke where the motion of the contact at 'the beginningof thecontact opening interval is substantially unimpeded so that desirablyhigh velocities 1 can be'obtained'during the initial contact openingperiod,

and at the same time,'the movable contact is subjected to pneumaticfo'rccsin such a manner as to prevent the generation of shock waves.

More specifically, the movable contact is provided with a piston whichmoves within a cylinder. The piston defines two volumes. The first spaceis normally in communication within the interior of the contactcontainer, and its pressure will remain relatively independent of thevolume defined by the piston as the piston moves within the cylinder.The second space, however, on the other side of the piston is connectedto areas within the interrupter container by a small orifice whereby, asthe movable contact is moved to its disengaged position, this latterspace will increase so that the pressure of the space is 3,134,875Patented May 26, 1964 decreased. The force driving the movable contactis, therefore, a function of the differential pressure on either side ofthe piston where one of these pressures is relatively constant, whilethe other pressure is a constantly decreasing pressure. Therefore, themotion of the contact is controlled due to a decrease in pressure on thedriving side of the piston rather than by causing the piston to driveagainst an increasingly higher pressure air cushion whereby bouncingproblems are better controlled.

Accordingly, a primary object of this invention is to provide a novelmeans for controlling the motion of the movable contact of an air blastcircuit breaker.

Another object of this invention is to provide novel means for thecontacts of an air blast circuit breaker which will decrease thevelocity of the movable contact prior to the time that the movablecontact reaches a fully disengaged position.

Another object of this invention is to prevent rebound of the movablecontact of an air blast circuit breaker.

A still further object of this invention is to decrease the kineticenergy of the movable contact in an air blast circuit breaker when themovable contact reaches the end of its opening stroke.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings inwhich:

FIGURE 1 shows a cross-sectional view of the contact structure of anairblast circuit breaker constructed in accordance with the presentinvention. Y

FIGURE 2 graphically illustrates the contact position of the movablecontact of FIGURE 1 as a function of time in solid lines, as contrastedto the prior artl ype movable contact illustrated in dotted lines.

' FIGURE 3 shows the contact velocity-of the movable contact of FIGURE 1as a function of time in solid lines as contrasted to the prior typedevices illustrated in dotted lines.

Referring first to FIGURE 1, I have shown the main breaking'gap of atypical air blast circuit breaker which includes an insulating container1 which carries a stationary contact 2 (partially shown), and a movablecontact 3 formed of a conductive tubular member having opening 4 whichextends centrally through movable con- I tact'3.

An upper conductive cap is secured to'container land has an orifice 5atherein which is in communication with the external atmosphere. Aflexible'insert 5 is at the top of the cap for receiving the upperend ofcontact 3 when contact 3 is moved to its disengaged position. Thus, whencontact 3 is moved to its disengaged position, the interior of container1 is sealed with respect to opening 5a so that compressed air is notlost from the interior of container 1. I a

Movable contact 3 is biased toward its closed position shown in FIGURE 1by a compression spring 6. The

movable contact 3 is then provided with an outercollar or flange whichserves as a piston in accordance with the present invention, and ismovable within cylinder 8.

Th'e piston 7 defines a space 9 within cylinder 8 which,

during the opening motion of movable'contact 3, will'be increased.

Piston 7 defines a space 9 within cylinder 8 which is in communicationwith the interior of the container through the small orifice 10, whereasrelatively large openings 11 permit ready communication between space 12and the space enclosed by container 1.

As shown in dotted lines in FIGURE 1, movable contact 3 contains arelatively small channel 13 which communicates between space 9 and thespace enclosed by container 1 which would include space 12 withincylinder 8. Note that channel 13 is cut on from this external space whencontact 3 moves a predetermined small dismoves downward. These backvalve means and the restricted opening 10 can of course be locatedotherwise.

In order to move the contact 3 to its disengaged position, a source ofrelatively high pressure air is connected to container 1. The contact 3then begins to move up:

wardly, since the pressure on the exposed portion not covered by contact2 is great enough (because the pressures 7 in spaces 9 and 12 are equal,by virtue of passage 13) to exceed the strength of spring6.

Once this movement has started, high pressure air will flow fromcontainer 1 through channel 4 and through orifice a to break the arcbetween contacts 2 and 3.

Continued movement of the movable contact 3 closes oif the passage 13.However, the whole bottom area of thecontact 3 except for the passage 4is now exposed to air .pressure while the upper part is in contact withfree air. The pressure on the exposed end of the contact 3 is enough toovercome the resistance of spring 6.

As the contact moves upward, with passage 13 closed, the space 9enlarges. This means, because thehigh pressure air can only enter thespace 9 slowly because of restricted orifice 10, that the pressurewithin the space 9 tends to decrease with respect to that in space 12.This means that thenet force acting on the bottom of piston 7 plus theforce acting on the bottom of contact 3 tends to come to a balance withthe force acting on the top of piston 7 plus the force of spring 6.However, because the orifice 10 does permit slow flow into space 9,tending to balance the pressure on both faces of the piston, the member3 will continue to moveupwardly to'its uppermost position, but will movemore slowly than if -space 9 was in free communication with the interiorof container 1.

The final velocity of the movable contact is thus substantiallydecreased at the end of the motion of the contact so that, asthe upperend of contact 3 seats against member 5, to seal off channel 4 fromorifice 5 there will be a minimum of bounce.

When the uppermost position is reached, the pressure onthe bottom of thecontact 3 is still greater than the force of spring 6, because thesurfaces of the movable contact are suitably proportioned so that thiscondition exists, and the pressure is equalized on the opposite sides ofpiston 7, so that the movable contact is held in disengaged position bythe pressure in the container.

When the pressure is removed from container 1, contacts 2 and 3 areclosed by the influence of spring 5 with the check valve means 14preventing the compression of air in space 9 so that the closing motionof contact 3 is not retarded. That is, during downward movement of thecontact 3, check valves 14 will open so that the move- 'ment of thepiston is not substantially retarded by reason of the restricted opening10.

In FIGURE 2 I have illustrated the relationship between time and contactposition for the case of the usual 'type of circuit breaker contactshown in dotted lines, while the novel control structure of the presentinvention is shown in solid lines. It will be seen in FIGURE 2 that whenusi g the c n o m n o the in enticn he contact opens at a time laterthan is the usual case. However, during the critical period in which thecontact is initially moved, there is substantially no difference betweenthe characteristics of the usual type of circuit breaker contact and thecircuit breaker contact of the present invention. As a consequence ofthis increase in time, and as shown in FIGURE 3, the contact velocityduring time decreases from its peak value, whereby the kinetic energy ofthe movable contact at the end of the opening stroke is considerablyless than in the case of the prior art type structures shown in dottedlines in FIGURE 3.

More specifically, in the case of FIGURE 3, the final contact velocityis less than /2 of the usual final velocity, whereby the kinetic energyof the movable contact will be less than A that contained by a contactdriven by prior art means.

In the foregoing, I have described my invention only in connection withpreferred embodiments thereof. Many variations and modifications of theprinciples of my invention within the scope of the description hereinare obvious. Accordingly, I prefer to be bound not by the specificdisclosure herein, but only by the appended claims.

I claim:

1.'A contact velocity control means for an airblast circuit breakerhaving a contact movable between engaged and disengaged positions and acontainer adapted to be filled with airunder pressure, said contactbeing movably mounted in the container, said control means comprising acylinder element and a piston element slid- -able in the cylinderelement, said piston element defining first and second spaces within thecylinder element on opposite sides of the piston element, one of saidelements being secured to the container and the other to the-movablecontact, said first space being substantially closed off from theinterior of the container, said first space inpassage.

2. In a contact velocity control means as claimed in claim 1, meansindependent of said restricted opening connecting said second space withthe interior of the container in the engaged position of the movablecontact,

and means operable by movement of the movable contact away from itsengaged position to close said connecting means.

References'Cited in the file of this patent UNITED STATES PATENTS2,015,792 Geraghty Oct. 1, 1935 2,025,549 Prince "Dec. 24, 19352,572,406 ,Stulz Oct. 23, 1951 2,574,334 Latollr NOV. 6, 1951 2,592,079Thommen et a1. Apr. 8, 1952 2,919,329 Latour Dec. 29, 1959 3, 71, 7Yeckl y et a1, an. 1, 1 6.

1. A CONTACT VELOCITY CONTROL MEANS FOR AN AIRBLAST CIRCUIT BREAKERHAVING A CONTACT MOVABLE BETWEEN ENGAGED AND DISENGAGED POSITIONS AND ACONTAINER ADAPTED TO BE FILLED WITH AIR UNDER PRESSURE, SAID CONTACTBEING MOVABLY MOUNTED IN THE CONTAINER, SAID CONTROL MEANS COMPRISING ACYLINDER ELEMENT AND A PISTON ELEMENT SLIDABLE IN THE CYLINDER ELEMENT,SAID PISTON ELEMENT DEFINING FIRST AND SECOND SPACES WITHIN THE CYLINDERELEMENT ON OPPOSITE SIDES OF THE PISTON ELEMENT, ONE OF SAID ELEMENTSBEING SECURED TO THE CONTAINER AND THE OTHER TO THE MOVABLE CONTACT,SAID FIRST SPACE BEING SUBSTANTIALLY CLOSED OFF FROM THE INTERIOR OF THECONTAINER, SAID FIRST SPACE INCREASING IN VOLUME DURING MOVEMENT OF THECONTACT TOWARDS DISENGAGED POSITION, A RESTRICTED OPENING CONNECTING THEFIRST SPACE TO THE INTERIOR OF THE CONTAINER, SAID SECOND SPACE BEING INSUBSTANTIALLY FREE COMMUNICATION WITH THE INTERIOR OF THE CONTAINER,SAID MOVABLE CONTACT HAVING A PASSAGE THERETHROUGH COMMUNICATING WITHFREE AIR, SAID PASSAGE OPENING WHEN THE CONTACT STARTS TO MOVE TODISENGAGED POSITION, AND MEANS OPERABLE WHEN THE CONTACT REACHES FULLYDISENGAGED POSITION TO CLOSE SAID PASSAGE.